Method of working metal



Dec. 4, 1934. v F. MOHLER 1,983,387

METHOD OF WORKING METAL Filed June 15, 1951 lllllllllll M||||||||I|Illlllllll Fig. 2

Inventor: Ffancis Mohlen,

by mym His Attorney.

' Patented Dec. 4, 19 34 1,983,387 METHOD OF WORKING METAL FrancisMohler,

General Electric Company,

, New York Schenectady, N. Y., assignor to a corporation of ApplicationJune 15, 1931, Serial No. 544,520

6 Claims.

This invention relates to metal working. more particularly to theproduction by the cold rolling process of exceedingly thin steel strip,such for example as commercial tin plate, and it has for 5 an object theprovision of an improved method for effecting substantial uniformity ofthickness or gauge in the finished strip.

Cold strip steel is usually rolled in a continuous mill having aplurality of tandem disposed sets of reducing rolls and a take-up rollupon which the finished strip is wound; each set of rolls and thetake-up roll being driven by a suitable driving means, such for exampleas an electric motor.

Heretofore, it has been even necessary to the strip between believeddesirable and maintain constant tension in the successive stands of theprocess in order to obtain the finished strip. In accordance with thisbelief, the reducing rolls of the several stands of the mill have beenreinforced by large backing rolls so as to apply a large compressionalforce to efiect the necessary reduction in gauge, and the separate standdriving motors have been compounded for a drooping speed characteristicin order to maintain the tension in the strip constant. Constant betweenstands substantially tension regulators, in reality constant currentregulators, have also been employed to maintain constant input to themotors and constant tension in the strip by varying the speed of themotors in response to the load thereon.

changes in Up to the present-time, however, it has not been possiblewith control in cold rolling the known methods of tension in acontinuous rolling mill to produce finished strip in. the thinner gaugesof materia having a uniformity limits.

The cold strip, tion, is a product e. g., commercial tin plate, of gaugewithin the desired prior to the cold rolling operaof a hot strip milland the undesirable unevenness or non-uniformity of gauge of the finished cold strip is believed to be due to the presence of relatively hardand soft or thick spots which form in the material during cooling of thehot strip,

and which during the cold rolling operation cause-the cold strip millrolls to sprin g and the bearings to give when a hard spot enters therolls. If there were no spring in the rolls of the cold strip mill thegauge of the finished strip would necessarily be absolutely uniform. As

long as the material which enters the rolls of a cold strip mill isofuniform thickness and hardness, the spring of the rolls is likewiseuniform and the gauge of the finished rolled ever, when a hard the rollsspring to pending upon the strip is also uniform. Howor thick spotstrikes the rolls, a greater or lesser degree dedegree of hardness andthe 'size of, the hardened area. The rolls commonly employed in a coldstrip rolling mill are approximately twenty inches in diameter and thesein turn are reinforced by backing rolls as large as forty-eight inchesin diameter. Further increase in the size or weight of the rolls wouldtherefore appear to be decidedly impractical and consequently little ifany improvement in the uniformity of gauge of the finished strip can beexpected from improvements .in the structure of the rolls.

I have definitely determined that variations in the tension applied tothe strip during the rolling operation greatly affect the gauge of thefinished strip.

Accordingly a further object of this invention is to control the tensionof the strip during the rolling operation so as to produce uniformity ingauge of the finished cold strip. In carrying the invention into effectin one form thereof, a tensional force is applied to the strip and thistensional force is varied in accordance with the degree of hardness ofthe strip.

More specifically a relatively small tensional force is applied to thestrip as it passes through the rolls at the successive stands of themill and this tensional force is increased at the instant that a hardspot in the strip strikes the rolls at any particular stand.

For a better and more complete understanding of the invention, referenceshould now be had to the following specification and to the accompanyingdrawing in which Fig. 1 is a diagrammatical illustration in verysimplified form of a continuous cold strip rolling mill; and Fig. 2 is asimple diagrammatical representation of an embodiment of a controllingand regulating system for the motors employed in carrying out theinvention.

Referring now to the drawing, a cold strip of steel 10 is shown aspassing in the direction of the arrow through the reducing rolls 11, 12at one stand of a cold strip rolling mill. The guage or thickness of thestrip 10 is materially re-. duced as it passes between the rolls 11, 12and the strip is then passed between the rolls 13, 14 at the nextsucceeding stand of the mill where the gauge is still further reducedafter which the finished strip is shown as being wound upon a take-uproll 15. Although but two stands have been illustrated in the drawing,it will, of course, be understood that a greater number of stands isusually employed in actual practice.

The reducing rolls 11, 12 and 13, 14 are driven by any suitable drivingmeans, such for example as electric motors 16 and 1'7 to the drive shaftof which the pairs of rolls 11, 12 and 13, 14 are respectively connectedby any suitable speed reducing means represented in the drawing by thedotted lines 18, '19. Similarly the take-up reel 15 is driven by meansof an electric motor 20 to which it is suitably connected as illustratedin the drawing.

The motors 16, 17 and 20 are preferably direct current motors of theshunt wound type and are designed to have very slight drooping speedcharacteristics with respect to wide variations in load thereon.

Although the motors 16, 17 and 20 may be supplied from any suitablesource of power, they are preferably supplied from a Ward- Leonardsupply generator 21 to the armature of which the armatures of the motors16, 17 are connected in a closed loop by means of the conductor 22,supply busses 23 and supply leads 24 and 25 respectively. TheWard-Leonard generator 21 is driven at a speed which is preferablysubstantially constant by any suitable driving means such for example asthe alternating current motor 26, which, as shown, is supplied from anysuitable source of power such for example as that represented in thedrawing by the three supply lines 27.

The generator 21 is provided with the usual field winding 28 which issupplied from any suitable source of excitation such for example as theexciter 29, the armature of which is connected to excitation busses 30to which the field wind- ,ing 28 is also connected by means of theconductors 31 as shown.

Exciter 29 is driven at a speed which is preferably substantiallyconstant by any suitable means such for example as the alternatingcurrent motor 32 supplied from a suitable source of power represented inthe drawing by the three supply lines 33, which source may be, andpreferably is, the same as that represented in the drawing'by the threesupply lines 27.

As shown, the exciter 29 is provided with a self-excited field winding34 connected across its armature terminals with a variable resistance 35included in circuit therewith. The voltage generated by the exciter 29and supplied to the excitation busses 30 is adjusted to any desiredvalue by altering the position of the movable contact 35a on thevariable resistance 35 as is well understood by persons skilled in theart The stand driving motors 16 and 17 are respectively provided withfield windings 36 and 37 which are supplied from the excitation busses30 to which they are respectively connected by means of the connections38 and 39. 4

A variable resistance 40 is included in circuit with the field winding28 of the Ward-Leonard supply generator 21 and, as is well understood,the voltage generated by the generator 21 may be controlled at will byvarying the position of the movable contact 40a on the resistance 40 toincrease or decrease the degree of excitation of the field winding 28depending upon whether the movable contact 409. is moved in a directionto increase or decrease the amount of the resistance 40 in circuit withthe field winding 28. Since the speed of the stand driving motors 16 and17 vary the Ward-Leonard supply generator 21.

Although any suitable form of speed regulating devices may be employedfor maintaining the speed of the stand driving motors 16, 17substantially constant at any desired value, the differential motiontransmission system shown in the drawing is preferably employed becauseof the high degree of accuracy with which it functions to maintain thedesired speed. In this system variable resistances 41 and 42respectively connected in circuit with the field windings 36, 37 of thestand driving motors 16, 17 are respectively controlled by electricaldifierential motion devices 43 and 44 which in turn are actuated inaccordance with the speed of a master motion transmitting device 45 andindividual motion transmitting devices 46 and 47 respectively associatedwith the stand driving motors .16 and 17.

The master motion transmitting device 45 comprises a stator member 45awhich is provided with a polycircuit winding (not shown) which isphysically similar to a polyphase alternating current winding and arotor member 45b which is provided with a single phase winding (notshown) arranged in inductive relationship with the stator winding; theterminals of the polycircuit winding being connected to the bussesrepresented in the drawing by the three conductors 48, and the singlephase winding on the rotor 45b being supplied with single phasealternating current from any suitable source such as that represented inthe drawing by the two supply lines 49 with which its terminals areconnected by means of the conductors 50. The rotor member 45b of themaster device 45 is rotated at a speed which is proportional to thespeed at which the stand driving motors 16 and 17 rotate, by means of asmall electric motor 51 the armature member of which is supplied fromthe Ward-Leonard supply generator 21 to the supply busses 23 of whichthe motor 51 is connected by means of conductors 52. In order that theinitial speed of the master motor 51 may be made to correspondaccurately with the speed 01' the stand driving motors 16 and 17; avariable resistance 53 is included in circuit with the field winding 51:which as shown is supplied from the excitation busses 30.

The individual motion transmitting device 46 which is associated withthe stand driving motor 16 is in all respects similar to the mastermotion transmitting device 45 and consists of a stator member 46.provided with a polycircuit winding (not shown) and a rotor member 46bwhich is provided with a single phase winding (not shown) arranged ininductive relation with the polycircuit winding on the stator member469. and supplied from the same single phase source 49 as that fromwhich the single phase winding on the rotor member 45b of the mastermotion transmitting device is supplied. As shown in the drawing, therotor member 463 is driven from the shaft of the stand driving motor 16to which it is mechanically coupled by means of a suitable variablespeed transmission device shown in the drawing as consisting of a conepulley 54 on the drive shaft of the motor 16 and a similar butoppositely arranged cone pulley 55 mounted on the shaft of the rotormember 46b, together with a belt-56 which is arranged to be slid in onedirection or another along the surfaces of the cone pulley so that thespeed of rotation of the rotor member 46 can be made to accuratelycorrespond with the speed of the rotor member 45b of the master motiontransmitting device 45 when the stand driving motor 16 is rotating atthe desired speed.

The electrical difierential' motion device 43 associated with the standdriving motor 16 comshall exist in the strip 10 between prises a statormember 433 which is provided with a polycircuit winding (not shown) theterminals of which are connected to the terminals of the polycircuitwinding arranged on the stator member 46a of the individual motiontransmitting device 46, and a rotor member 43b which is likewiseprovided with a polycircuit" winding (not shown) arranged in inductiverelationship with the polycircuit winding on the stator member 43a andconnected to the busses 48 by means of conductors 57. ing on the rotormember 46b of the individual motion transmitting device and the windingon the rotor member 45b of the master motion transmitting device aresupplied with an alternating voltage, it will be understood thatalternating voltage will be induced in the polycircuit winding on thestator member 46a of the individual device and the winding on the statormember 45a of the master device and that these alternating voltages arerespectively supplied to the polycircuit winding on the stator member439. and the polycircuit winding on the rotor member 43b of thedifferential device.

Persons skilled in the art will understand that as long as theelectrical axes of the single phase winding on' the rotor members of theindividual motion transmitting device 46 and the master motiontransmitting device 45 are in angular agreement, the voltages suppliedto the polycircuit winding on the stator member 43a and on the rotormember 43b ill balance each other, i. e., they will be exactly equal andopposite and consequently there will be no tendency for the freelyrotatable rotor member 43b to move with respect to the stator member43a.

Although the variable resistance 41 in the field circuit of the standdriving motor 16' may be of any suitable type a pressure responsiveresistance, such for example as the stack of carbon discs illustrated inthe drawing is preferably employed. The carbon pile 41 is arrangedbetween a suitable stop 41a and one extremity of a lever 58, theopposite extremity of which is turned in either direction about thefulcrum 583 by means of a cam 59 which as shown is connected to therotor member 43b of the differential device 43 by any suitableconnecting means such for example as the worm and the worm wheel 60.

As is evident from the drawing, the speedregulating device for the standmotor 1'7 is in all respects identical with that just described and itis, therefore, believed to be unnecessary to repeat a detaileddescription of the regulating device for motor 17.

In operation the mill motors 16, 17 are accelerated from rest by varyingthe field excitation of the ward Leonard supply generator 21 and afterthe mill motors 16, 17 have been brought up to speed the strip 10 isthreaded between the rolls 11, 12 and then carried along by the operatorand threaded into the rolls 13, 14 of the finishing 'stand. Theexcitation of the motor 51 which drives the master motion transmittingdevice 45' is increased until the speed of .the rotor 45b correspondsaccurately with the speed of the rotors 46b and 47b of the individualmotion transmitting devices 46 and 47 respectively; this condition ofspeed correspondents being indicated by the rotor members 43b and 44b ofthe differential devices coming to rest.

In order that only a very small tensional force the pairs 01 Since thesingle phase windstand rolls 11, 12 and 13, 14 a large loop may beformed in the strip 10 after it has been threaded through the rolls 11,12 and before it is threaded into the finishing rolls 13, 14. An ammeterplaced in the armature circuit of the stand driving motor 17 may be readto ascertain the current necessary to reduce the gauge of the strip atthis point solely by the compressional force exerted on 13, 14. Similarobservation taken at the other stands of the mill under similarcircumstances will indicate the amount of current input to each standdriving motor necessary to reduce the strip at each particular standsolely by the compressional force exerted on the strip by the rolls andwithout the aid whatsoever of any tensional force in the strip.Thereafter when the rolling process has begun, the belts 56 and 61 areshifted in one direction or the other upon the cone pulleys of the speedregulating devices until the readings of the ammeters correspond withder the condition of no tension in the strip 10 and the reductionthereof being affected solely by the compressional force of the rolls atthe various stands.

In actual practice the belts 56 and 61 of the speed regulating devicesare shifted until the input to the various stand driving motors 16, 17are slightly higher than thoseobserved under the condition of no tensionin the strip, and this will insure a slight tension in the strip be-.tween the rolls of the various stands which is of course materiallyless than the elastic limit of the material, but which is neverthelesssufficient to maintain a certain desirable tautness in the strip duringthe rolling operation.

As long as the texture, i. e., the degree of hardness of the strip 10entering the rolls 11, 12 is uniform the reduction of the gauge of thestrip by the rolls 11, 12 will be done principally by the compressionalforce exerted by these rolls and the gauge of the strip leaving therolls will for all practical purposes be substantially uniform. However,if a portion of the strip 10 entering the rolls 11, 12 is considerablyharder than adjacent portions thereof, the rolls 11, 12 will tend tospring apart slightly and as a result the elongation of the strip atthis point will tend to decrease, i. e., the forward linear the strip bythe rolls the readings previously taken unv speed of the strip 10-at thenip of the rolls 11,

12 is slightly retarded. This retardation in the speed of the strip 10at the rolls 11, 12 imposes an increased load on the motor 17 whichdrives the rolls 13, 14 at the next succeeding stand and, as a result,the speed of the motor 1'? tends to decrease slightly. As the speed ofthe motor 1'7 tends to decrease, the angular correspondence between theelectrical axes of the rotor members 45b and 47b of the master andindividual motion transmitting devices respectively is disturbed, andconsequently the voltages supplied to the polycircuit vice 44 becomeunbalanced, thus causing the rotor member 44b to rotate The above descriregulating action takes relatively to the statormember 443, therebycausing the cam 62 to be windings of the differential deplaceexceedingly rapidly, 'imfact almost instantaneously, and consequentlythe speed of the motor 17 is for all practical purposes maintainedconstant continuously at the desired value. Since the speed 01' themotor 17 is held constant and cannot decrease in response to theincreased load when a hard spot in the strip strikes the rolls 11, 12,the input to the motor 17 naturally must increase in order to sustainthe increased load and this increased input increases the tensionalforce in the strip between the rolls 11, 12 and the rolls 13, 14. Theincreased tension force in the strip is most effective at the point inthe strip which is subjected to the compressional force between therolls, i. e., is most efiective at the hard spot in the strip, and thisincreased tensional force taken in combination with the compressionalforce due to the rolls 11, 12 is suiiicient to reduce the hard spot, sothat the gauge of the strip emerging from the rolls 11, 12 is of thedesired value, despite the tendency of these rolls to spring as the hardspot in the strip enters.

The increased input to the motor 1'7 and the increase in tensional forcein the strip is directly proportional to the texture of the strip, i.e;,the degree of hardness thereof, and thus the elongation of the strip issubstantially constant and the gauge of the strip as it emerges from therolls 11, 12 has the desired uniformity. After the hard spot in thestrip has been reduced, the load on the motor 17 is decreased and thespeed of this motor naturally tends to increase above normal value. Thespeed regulating mechanism, however, responds to this tendency toincrease in speed and functions in the reverse manner to that previouslydescribed, to

increase the field current of the motor so as to maintain its speed-atnormal value. As a result the input to the motor is lessened and thetensional force applied to the strip is likewise decreased inproportion.

Since similar constant speed regulators are provided for the motors atall the stands in the mill, the above-described operation also takesplace atother sections of the mill when a hard spot in the strip strikesa pair of rolls at any particular stan It will thus be clear that aslong as the texture, i. e., the degree of hardness 'of the strip isuniform, the reduction in gauge atthe various stands is accomplishedprimarily by the compressional force of the rolls and that the ten--sional force in the strip between any-two successive stands ismaintained at a value which is considerably less than the elastic limitof the metal and which is l'or all practical purposes negligible, whilstwhen a hard spot or portion of the strip engages theorolls at anyparticular stand, the tensional force in the strip between *this standand the next succeeding standis increased in proportion to the degree ofhardness of this hard spot or portion of the strip.

Persons skilled in the art will understand that ,due to the inherenttendency of a shunt wound machine to maintain-constant speed despitevariations in load, the above described operations and results can beapproximated though not equaled, without using any special constantspeed regulating apparatus simply by employing shunt wound motorsdesigned to have an almost negligible drooping speed characteristic fordriving the rolls at the various stands of the mill. Although, inaccordance with the provision of the patent statutes, I have describedthe invention as embodied in concrete form and as being carried out in aspecific manner, I would have it understood that the description ismerely illustrative and that the invention itself is by no means limitedthereto since alterations and modifications will readily suggestthemselves to persons skilled in the art without departing from the truespirit of the invention as set forth in the annexed claims.

- What I claim as new and desire to secure by Letters Patent of theUnited States, is:

1. The method oi. working cold metal that comprises applying to saidcold metal a tensional force and a substantially constant compressionalforce, and passing the cold metal through thickness reducing means at.substantially constant speed, thereby to vary said tensional force inaccordance withxvariations in the texture of the metal.

2. The method of working cold metal that comprises applying to saidmetal while cold a relatively large compressional force and a relativelysmall tensional force, and passing said metal while cold throughthickness reducing rolls at susbtantially constant speed to increasesaid tensional force with increasing hardness of the portion of themetal engaged by the rolls.

3. The method of working cold metal that comprises applying to saidmetal while cold a compressional force and a relatively small tensionalforce, passing said metal while cold through reducing rolls, andmaintaining the speed of said rolls substantially constant, thereby tomaterially vary accordance with variations in metal. a

4. The method of working cold metal that comprises applying to saidmetal while cold a compressional force in the neighborhood of theelastic limit of the metal and a tensional force materially less thanthe elastic limit thereof, passing said metal while cold through gaugereducing rolls, and materially increasing said tensional force when arelatively hard portion of the metal enters said rolls by maintainingthe speed of said rolls substantially constant. 5. The method of workingcold metal that comprises applying a compressional force and a tensionalfarce to said metal while cold, passing said metal while cold throughthe reducing rolls of each of a plurality of successive stands, andmaterially varying the tensional force between successive stands when arelatively hard portion of the metal enters the rolls of one of saidstands by maintaining the speeds of the rolls of all of said standssusbtantially constant.

6. The method 01' working cold metal that comprises applying to themetal while cold a relatively large compressional force and a relativelysmall tensional force, passing the metal while cold between reducingrolls of a plurality of successive pairs of rolls, and maintaining thespeeds of all of said pairs of rolls substantially constant tomaterially increase said tensional force between one stand and asucceeding stand when a relatively hard portion of the metal enters therolls of said one stand.

FRANCIS MOHLER.

the texture of the said tensional force in

